Contact areas are used to enable an electrical plug connection between a connector and mating connector, and to conduct current accordingly. In automotive applications in particular, tin, gold, or silver surfaces are used for the surfaces of the electrical contact areas. These are hot-galvanized or electroplated layers in the range of a few micrometers, which are applied onto a support material, for example a circuit board. The layers themselves have properties of deformability and good electrical conductivity.
At the interfaces to typical copper-based alloys, for example bronze, that often serve as the basic material for electrical plug connections, diffusion results in the formation of an intermediate layer that is made of intermetallic compounds, e.g. Cu3Sn or Cu6Sn5. This intermediate layer is harder, and can grow as a function of temperature.
Several other alloys based on the elements recited above may be found, for example SnPb, SnAg, SnAgCu, AuCu0.3.
Tin alloys, in particular, have low hardness and therefore also little wear resistance; as a result, frequent insertion/removal, or vehicle or engine-related vibrations can very easily cause the contact surface to be rubbed through, which in turn means that the plug connection has a tendency toward oxidation, i.e., so-called fretting corrosion. As a result of this rubthrough and/or the corresponding fretting corrosion, failures of important electrical components can cause disruptions to the operation of a motor vehicle.
Another disadvantage is that the aforementioned alloys have very high adhesion tendencies, so that the insertion forces that must be applied in order to establish an electrical plug connection are very high. The plastic deformation associated therewith is also too great for many applications. The adhesion can in fact cause the layer to be torn off or transferred, or to become chipped.
Similar processes can also occur with gold and silver surfaces if the contact surface is rubbed through and the material located beneath is correspondingly oxidized.